Stability issues of Cu(In,Ga)Se-2-based solar cells

Stability aspects of the Mo/Cu(In,Ga)Se-2/CdS/ZnO solar cell are reviewed a nd assessed. These include (i) the chemical stability of the various interf aces present in the device, (ii) the long-term behavior of metastable defec ts found in the Cu(In,Ga)Se-2 (CIGS) compound, and (iii) the impact of Cu m igration on device performance and lifetime. We find that (i) all interface s within the structure are chemically stable, (ii) metastable defects have a beneficial effect on performance, and (iii) Cu migration effects are reve rsible and their possible detrimental effects are eclipsed by the beneficia l effect of the metastable states. Moreover, Cu out-diffusion from the CIGS layer is absent in photovoltaic-quality CIGS. Finally, we propose a model that explains the exceptional radiation hardness and impurity tolerance of CIGS-based devices, based on the synergetic effect of copper migration and point defect reactions.